Basalt fibers were dip-coated in zirconium-n-propoxide, unstabilized or stabilized by chelation with ethyl acetoacetate. The thermal transformations of the hydrated zirconia coatings formed were investigated by dynamic x-ray diffraction and differential thermal analysis. The changes in the surface chemical compositions of coated and uncoated fibers, following alkali immersion extending to 90 days, were characterized by EDXA and IR spectral analysis. Fiber strengths were also measured after immersion in 0.1 M NaOH for different durations. It was found that the transition of the amorphous zirconia coating to the tetragonal crystalline phase is shifted to higher temperatures by chelation of the zirconium alkoxide. Alkali corrosion of the uncoated basalt fibers results in dissolution of the oxides of Si, Al, and Ca, and the formation of unsoluble hydroxides of Fe, Mg, and Ti from the chemical constituents of basalt. These reactions are suppressed by the protective zirconia coating on basalt fibers formed by the unstabilized zirconium alkoxide. However, the coating formed from zirconium propoxide stabilized by ethyl acetoacetate does not form an effective barrier against alkali attack since it is easily detached from the fiber surface during alkali immersion. The tensile strength of uncoated basalt fibers is drastically reduced by alkali attack. But the strength of zirconia-coated basalt fibers is maintained even after 90 days of alkali immersion. The vastly improved alkaline durability of the coated fibers shows the potential of zirconia-coated basalt fibers for cement reinforcement.

Sols of titania were obtained by the sol-gel method and their size profile was followed by dynamical light scattering. In the early stages of the reaction an unstable behavior was detected. After this unstable regime the particle size reaches a steady state where the sols have a constant size while increasing in number. Once the sol concentration reaches its overlap value, the gelation regime takes place. For samples prepared in this way Raman spectra and x-ray diffractometry were used to characterize the kinetics of crystallization of the material.

ZnO seed grains are derived from washing ZnO-BaO sintered disks in boiling water. The grain growth of ZnO results from the energy difference across a curved grain boundary. The growth dynamics of ZnO grains and the dissolution of BaO in the boiling water are studied. The classical model shows that the growth of ZnO grains depends on grain boundary diffusion. The dissolution of BaO in boiling water can be considered as the diffusion of BaO in boiling water. The weight percent of BaO dissolved in boiling water varies linearly with the thickness of ZnO-BaO sintered disks and the reciprocal of the square root of the boiling time.

Rheotaxial growth and thermal oxidation (RGTO) for depositing thin films is a recognized technique in preparing gas sensitive semiconducting oxides. This paper presents a study performed by x-ray diffraction and scanning Auger microscopy of the mechanisms of growth and formation of the thin films of the new ternary compound Sn1−xFexOy with an iron content in the range O < x < 25 at. %. A structural model of this compound, which is found to be stable over a very large range of Sn/Fe ratios, can be derived by partially substituting Fe3+ ions in Sn4+ sites. This is an easy substitution in view of the similar values shown by the ionic radii (Fe3+ = 0.64 Å, Sn4+ = 0.71 Å) and the Pauling electronegativity (Fe3+ = 1.8, Sn4+ = 1.8) of these two ions. Experimental data, showing that this material is an excellent CO sensor, are reported.

The phase chemistry and thermodynamics of the Ti-Si-N system are reviewed leading to a revision of the ternary phase diagram at 1273 K to include the extended compositional ranges of δ-TiNx and Ti5Si3(Ny) and the compounds Ti3Si, Ti5Si4, and α-Ti. This same information is presented in the form of phase stability diagrams which plot the stability criteria for each phase as a function of thermodynamic activity of one component and the relative composition of the other two components. Plots in terms of log asi vs Ti/(Ti + N), log aN2 vs Si/(Ti + Si), and log aTi vs N/(Si + N) were constructed. All diagrams are consistent with current knowledge of phase compatibility and, therefore, are topologically correct. Further refinement will be possible as more accurate information on thermodynamics and compositional limits of solid solutions becomes available.

The effects of annealing on B2O3-contained ZnO varistors with particular emphasis on the degradation behavior, nonlinear coefficient, trap density, donor density, and Schottky energy barrier were investigated. The thermal stability of ZnO varistors was considerably improved by the thermal annealing process.

Infrared absorption measurements have been used to study the radiation response of various hydroxyl point defects present in natural quartz crystals in their unswept, Na-swept, and H-swept conditions for “low-H” and “high-H” samples with similar aluminum concentration. The irradiation was done at 77 K, 300 K, and finally again at 77 K in sequence. At low-temperature irradiation the Al-OH− bands equalize in their intensity-like H-swept or prior 300 K-irradiated cultured quartz. Among other major bands the alkali-related centers show a reduction in their strength at all stages of irradiation. Purely H-related centers show no steady-state room temperature effects; only the low-temperature irradiation reduces their band strength. The results have been discussed in terms of proton and alkali ion motion to shallow and deep traps and compared with cultured quartz.

Cobalt phthalocyanine (CoPc) adsorbed on a carbon black support (Vulcan XC-72) and pyrolyzed at various temperatures is a potential catalyst for the reduction of oxygen in solid polymer electrolyte fuel cells. This paper reports the results of the microstructural characterization of β-Co particles that are formed after pyrolysis at temperatures of 700, 900, and 1050 °C. Transmission electron microscopy (TEM) indicated that (i) for a pyrolysis temperature of 700 °C, the size distribution of the Co particles is bell-shaped with an average value of 4 nm and mean deviation of 1 nm; (ii) for a pyrolysis temperature of 900 °C, the Co particle size distribution skews toward larger particle sizes. The most probable particle size is about 6 nm, and the average particle size is 13 nm. By comparison with the TEM results, the particle size estimated from a spectroscopic method like x-ray absorption is underestimated, while from x-ray diffraction is overestimated. The TEM images show that Co particles act as heterogeneous nucleation sites for the graphitization of amorphous carbon. It is shown that (i), at least for pyrolysis temperature of 900 °C and above, most of the β-Co particles are surrounded by a shell of graphitic carbon layers that appears to protect the particles from corrosion in acidic media; (ii) for pyrolysis temperature of 1050 °C, graphite strings also appear throughout the amorphous carbon support in areas where Co particles are not detected. This behavior was not observed after pyrolysis of as-received carbon support at 1050 °C. These results allow for a better understanding of the behavior of the pyrolyzed catalysts immersed in an acidic solution or in a solid polymer fuel cell.

This is a study of the form and structure of particles and particle aggregates of an experimental high surface area carbon black (HSA) using small-angle neutron scattering and the method of contrast variation. Contrast variation was effected by studying suspensions of the carbon black in cyclohexane containing different fractions of deuterocyclohexane. We find that the approximately 29 nm diameter USA particles are arranged as small, linear aggregates with an average aggregation number between 4 and 6. The structure averaged over the particle population is best represented by a prolate ellipsoid of revolution with semiaxes 14.5 and 76.4 nm. The surface of the aggregates appears smooth over length scales larger than 1 nm, which places an upper limit on the surface roughness observed by other methods. The internal structure of the aggregates is described by a shell-core model, with the shell density being consistent with a graphitic structure and the core being of lower density, more like amorphous carbon. Some fraction of the core volume (0.1 to 0.2) is taken up by voids that are not accessible to the solvent. An estimate of the shell thickness gives 1 to 2 nm along the ellipsoid minor axis and 6 to 10 nm along the major axis. The particles of the aggregate appear to be fused so that the less dense amorphous core is continuous through the inner parts of the aggregate. The information that can be obtained on the internal structure using contrast variation is limited by heterogeneity in the chemical composition of carbon black aggregates.

Powders of nanocrystalline aluminum nitride (AlN) and boron nitride (BN) were prepared via a chemical route. Precomposite gels, which were obtained from ammonolysis of aqueous solutions of boric acid, urea, and aluminum chloride hexahydrate, were thermally processed to produce AlN-BN nanocomposite powders with a wide range of compositions. These powders were characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). The structure, morphology, and crystallite size of the powders are correlated with the compositions and processing temperature. Normal and abnormal grain growth are discussed.

We have grown epitaxial thin films of rare-earth hexa-aluminates on basal plane sapphire from liquid precursors. LnAl11O18 (Ln = Gd3+, Nd3+) films form via the reaction of a perovskite intermediate phase and the sapphire substrate according to LnAlO3 + 5Al2O3 = LnAl11O18. Hexa-aluminate thin films with magnetoplumbite (MP) structure grow epitaxially with (0001)mp ‖(0001)s, 〈1120mp‖〈1010〉s orientation relationship. The a-axis of the film is rotated 30°with respect to the substrate. This rotation results in a smaller mismatch (∼1%) between the two oxygen sublattices. Thermodynamic and kinetic arguments pertaining to magnetoplumbite formation for the smaller Gd3+ cation are presented. These epitaxial thin films are likely to have application in higher temperature ion conduction, catalysis, fluorescence, and as laser host.

A simple electrochemical method is described for producing metal or semiconductor nanowires with diameters in the continuous range 10 to 200 nm. The technique involves a three-step process that begins with the electrochemical generation of an aluminum oxide template with uniform nanometer-sized pores, followed by the deposition of metal or semiconductor in them. The nanowires are then exposed for study or device fabrication by etching back the oxide matrix. Examples of cadmium nanowires fabricated by this technique are shown.

The influence of NaCl (3% of Cl−by weight of cement) on the reactivity of High Alumina Cement (HAC) in water has been studied over a period of one month. The changes in microstructure were monitored by x-ray diffraction and scanning electron microscopy. The pore-solution, extracted by the application of high mechanical pressure (500 MPa), was studied for the chemical composition and changes caused by chloride and sodium ions.

Fine particles of a hydrogen storage alloy (LaNi3.8Co0.5Mn0.4Al0.3) were microencapsulated with a thin film of nickel of about 0.6 μm thickness. The microencapsulated alloy powders were used as an anode material in a sealed nickel/metal hydride battery. The battery characteristics were compared with those of a battery with a bare (uncoated) alloy anode. The battery using the bare alloy was less stable compared to the coated alloy due to the role of the coated nickel as an oxygen barrier for protecting the alloy surface from oxidation. In addition, charge-discharge characteristics were improved greatly by the nickel coating, especially at high rates and at low temperatures due to the role of nickel as a microcurrent collector. So the microencapsulation of the alloy powders improves the performances of the alloy electrode.

The electrolysis treatment of the hydrothermal-electrochemical method has been modified so that it permits SrTiO3 thin films to be grown on Ti electrodes being oxidized anodically in Sr(OH)2 solutions far beyond a thickness limit of several tens of nanometers hitherto attained. The relation between the total current passed through the Ti anode and the amount of the resulting SrTiO3 film was analyzed on the basis of a reaction model that interprets the anodic current to be compensated with electrons generated partly by oxidation of Ti and partly by decomposition of H2O. Current efficiency for the film growth was estimated to be in the range from 0.8 to 3% depending on the Ti electrode potential.

X-ray photoelectron spectra of hydrated aluminas (boehmite, diaspore, bayerite, and gibbsite), transition aluminas (y, δ, η, θ, X, and k –Al2O3) and corundum (α-Al2O3) have been studied for spectral characterization of each compound. The O1s spectra are shifted 0.2–1.2 eV to higher binding energy (Eb) in the order of α-Al2O3 < boehmite, diaspore < bayerite, gibbsite, and this agrees with the order of bulk OH/Al molar ratio in samples. The Eb and FWHM values of O1s spectra of transition aluminas depend on the ratio OH/O, i.e., the amount of OH− ions chemisorbed on them, and tend to decrease toward those of α-Al2O3 with increasing calcination temperature. Therefore, it is considered that an attracting effect of the proton on valence electrons in the hydroxyl oxygen causes the increased binding energy between core electrons and oxygen atomic nuclei. The broad O1s spectra of boehmite and diaspore can be deconvoluted into equal contribution from the two oxygen species in O2− and OH− ions in their structures.

Surface-related characteristics (growth of surface layer and crystal preferred orientation) and the resulting mechanical strength of apatite-containing glass-ceramics in the system MgO–CaO–SiO2−P2O5 were investigated. The variations of surface-layer thickness and crystal preferred orientation were explained by a criterion considering both the surface and bulk nucleation of apatite phase. Glass-ceramics with a fairly high strength of 250–410 MPa could be obtained by an appropriate two-step heat treatment. The high strength in the present study is closely related to the growth of the surface layer, which might result in surface compressive-stress.

The microstructures of GaN films, grown on (001) and (111) Si substrates by a two-step method using Electron Cyclotron Resonance assisted-Molecular Beam Epitaxy (ECR-MBE), were studied by electron microscopy techniques. Films grown on (001) Si had a predominantly zinc-blende structure. The GaN buffer layer, grown in the first deposition step, accommodated the 17% lattice mismatch between the film and substrate by a combination of misoriented domains and misfit dislocations. Beyond the buffer layer, the film consisted of highly oriented domains separated by inversion domain boundaries, with a substantial decrease in the defect density away from the interface. The majority of defects in the film were stacking faults, microtwins, and localized regions having the wurtzite structure. The structure of the GaN films grown on (111) Si was found to be primarily wurtzite, with a substantial fraction of twinned zinc-blende phase. Occasional wurtzite grains, misoriented by a 30°twist along the [0001] axis, were also observed. A substantial diffusion of Si was seen in films grown on both substrates.

Various copper salts have been irradiated with the help of a continuous wave CO2 laser. In other experiments the same salts have been decomposed under a controlled heating rate, in a thermal balance, and copper oxide crystallites have been detected as the final product of both types of experiment. The measurements of crystallites performed with the help of x-ray diffraction exhibited differences between the two types of oxides: those obtained by laser irradiation as compared with the oxides obtained by thermal heating. The magnitude of this difference seems to depend on the laser quanta absorptivity of the initial salts. The results are consistent with those obtained previously on nickel oxides.

The system Y1−xSrxMnO3 (x = 0.000, 0.005, 0.010, 0.050, and 0.100) was studied as a potential cathode material for solid oxide fuel cells. Powders were prepared using an organometallic precursor; however, achieving homogeneous compositions was complicated due to the presence of intermediate, metastable phases. The desired hexagonal Y1−xSrxMnO3 phase formed from the precursor at 800 °C, while small amounts of a metastable orthorhombic (Y,Sr)MnO3 phase formed in the temperature range between 850°and 960 °C, and another orthorhombic YMn2O5 phase between 840°and 1200 °C. The metastable (Y, Sr)MnO3 phase readily transformed into the stable hexagonal phase at about 960 °C. The other metastable intermediate phase, YMn2O5, was formed as a decomposition product of a portion of the major hexagonal YMnO3 at 840 °C, and subsequently reacted with Y2O3 back to the hexagonal YMnO3 at 1200 °C. For the studied compositions, densities higher than 95% theoretical could be obtained by sintering in air at temperatures above 1400 °C for 2 h. The investigated system was comparable in electrical conductivity with the current cathode material La1−xSrxMnO3, and had an average apparent thermal expansion coefficient between 5 and 7 ppm/°C in the temperature range between 200°and 1000 °C. Unfortunately microcracking was observed in all sintered specimens, possibly caused by a high-temperature phase transition between the hexagonal and cubic polymorphs of Y1−xSrxMnO3. The microcracking presents a major obstacle to the use of this material as a cathode in solid oxide fuel cells.